A conventional CAES system 10, illustrated in FIG. 1, may include a gas storage unit 11 configured to store a process gas, such as ambient air, compressed by a compressor train 12. A feed line 13 may direct the compressed process gas from the gas storage unit 11 to a throttling device, such as a valve assembly 14, which may reduce the pressure of the compressed process gas. The feed line 13 may also direct the compressed process gas to a heat exchanger or recuperator 15, where the compressed process gas may be preheated, before being directed to an expansion assembly 16. The expansion assembly 16 may include an unfired expander or air expander 17, a fired expander 18, and a generator 19. The compressed process gas may be expanded in the air expander 17 to a reduced pressure. The expanded process gas may then be directed to a combustor 20 coupled to the fired expander 18, where the expanded process gas may be mixed with a fuel and burned before subsequent expansion in the fired expander 18. The expansion of the process gas in the air expander 17 and the fired expander 18 may drive the generator 19 to produce a power output. Exhaust gases from the fired expander 18 of the expansion assembly 16 may be pass through the recuperator 15 to preheat the compressed process gas from the gas storage unit 11.
The gas storage unit 11 of the conventional CAES system 10 may often include a cavern with sufficient volume or storage capacity to store the compressed process gas during off-peak hours. However, in many regions, geological constraints, such as a limited underground storage capacity or a lack thereof, may be imposed on the implementation of the CAES systems. In these scenarios, where the storage of the compressed process gas is limited or nonexistent, the amount of process gas utilized by the expanders 17, 18 to generate a power output, or specific air consumption, may be a critical factor in determining the overall efficiency and/or cost of implementing and/or operating the CAES system 10.
In view of the foregoing, above-ground storage devices are often utilized to store the compressed process gas during off-peak hours and overcome the geological limitations. Some conventional above-ground storage devices, however, may not provide suitable storage capacities, and other above-ground storage devices having suitable storage capacities may be cost-prohibitive.
What is needed, then, is a CAES system and method of operating thereof, capable of reducing the specific air consumption to increase efficiencies and costs of operating the CAES system.